[Explained] Wireless Charging: Everything You Need to Know

Time for Wireless Charging to go mainstream?

Most features on smartphones follow a trend of appearing first on flagships and then slowly trickle down to more affordable phones. We saw this happen with HD screens, fingerprint scanners, display notches, fast charging, and IP ratings. However, there’s one technology that for some reason has not yet been adopted in mid-range and budget-oriented smartphones, and that’s Wireless Charging. Wireless Charging is a feature that has existed on smartphones for almost a decade now. Samsung’s Droid Charge came with a replaceable back that had support for Qi wireless charging.

Samsung was one of the earliest adopters of Qi Wireless Charging and arch-rival Apple joined late to the party in 2017 with the iPhone X. While all this is still fairly new on consumer tech, wireless charging or wireless induction has existed for more than a century, thanks to Nikola Tesla who discovered that energy can be transferred wirelessly with the help of magnetism. While there are much bigger applications of wireless charging or magnetic induction in general, we are going to stick to the technology in smartphones keeping in mind the scope of this article.

How Does Wireless Charging Work?

Before we get into how your phone magically charges when you place it on a wireless charging mat or pad, let’s take a short trip down the memory lane to Class 10 Physics and try to understand the basics of magnetism and electricity. Let’s first begin with Alternating Current or what is more commonly referred to as AC. As the name suggests, in AC, the current does not flow in one direction, but it rather flows in two opposite directions alternatively. According to famous scientist Oersted’s experiments, electric current induces a magnetic field. The magnetic field depends on the direction in which the current is flowing, which means there will be different magnetic fields depending on the direction of the current.

Image: Cosmos Magazine

As we discussed earlier, in Alternating Current, the direction of current changes frequently. This means that the magnetic field produced by AC also changes as the direction of current changes rapidly. This change in the magnetic field produces electricity as discovered by Michael Faraday, and that is exactly the science behind wireless charging. If you think this was beyond your understanding, let’s look at it in a practical way, just the way it happens in real life.

Practical Working of a Wireless Charger

Your wireless charging pad has a coil buried not too deep behind the top surface. You would realize that most of the time, the top surface of a wireless charger is usually made out of plastic or wood or some sort of fabric. This is to allow the magnetic field to easily pass through. The same is the case with the material used on the back of the smartphone. Every smartphone that supports wireless charging will have either a glass or plastic back as metal does not allow induction to take place.

Image: epectec

Anyhow, getting back to the wireless charging pad, there is a coil that conducts electricity on the wireless charger itself, which is the transmitter, and there is a similar coil present on the back of a smartphone which acts as the receiver coil. On the wireless charging pad, the coil is connected to the AC mains through a power adaptor which converts it into DC and feeds it to the transmitter coil. The current then gets converted back to AC in the coil and there is a magnetic field that is induced. When a smartphone with a receiver coil is placed on the wireless charging pad, the transmitter coil induces AC into the receiver coil. The AC is then converted back to DC and is sent to the battery. This phenomenon is referred to as resonant inductive coupling.

Of course, there are other components in the wireless charger too like rectifiers, filters, etc. That helps in the conversion of AC to DC and other current controlling activities. There are some constraints involved here too, as we discussed earlier. The material on the surface of the wireless charger and the phone, distance between the transmitter and the receiver of the coil, size of both coils, etc. are factors that are important to enable wireless charging. This led to the rise of a standard that is followed by every smartphone manufacturer who has incorporated wireless charging in their smartphones – The Qi standard.

Qi Wireless Charging Standard

Qi is a wireless charging standard developed by the Wireless Power Consortium that can be used to interface any device with wireless charging. Manufacturers who incorporate the Qi standard have to attain relevant certification for their device to be Qi-compatible, be it smartphones or wireless chargers. Using the Qi standard, devices can be charged wirelessly for up to a distance of 4cm between the transmitter and the receiver coils.

Since these coils are further embedded behind other layers, the distance between a smartphone and the wireless charging pad has been reduced to millimeters. Basically, your phone’s surface should be touching the surface of the wireless charging pad for charging to take place.

Why is Wireless Charging so Slow?

This basically raises a debate that wireless charging is still not completely wireless due to the fact that the wireless charger itself always has to be plugged in and your phone has to completely rest on the wireless charger for it to work. Add to it the extremely slow charging speeds of around 5-10W on most common smartphones. The slow speeds are due to the fact that induction works better when the size of the coils is larger and the number of turns in the coil is more. Both these constraints are not possible to achieve on a smartphone due to the small footprint. Also, wireless charging involves a lot of power loss in the form of heat which again brings down the charging speed.

Present and Future Developments in Wireless Charging

Brands like Xiaomi, Huawei, and even OnePlus with the new rumored OnePlus 8 Pro have been working on custom wireless charging solutions that can go as high as 40W as supported by the new Mi 10 Pro. The OnePlus 8 Pro is supposedly going to come with support for 30W wireless charging. It sounds promising for sure, but it would be interesting to see how the adoption rate is as these fast-wireless chargers with support for 30-40W output are not easily available and if they are, they would be very expensive.

The future of wireless charging, when picturized in the most ideal and convenient manner, would be to get rid of the wired charging pad completely, and to increase the distance between the charger and the phone. There are alternatives to this too like a wireless charging power bank or wireless charging cases for select smartphones, but at the end of the day, even these gadgets will run out of juice and will need to be plugged in. Maybe you can just put your phone in your pocket one day and it can charge wirelessly? Who knows!

What’s good, though, is that apart from smartphones, more consumer gadgets like earphones and wearables are adopting wireless charging and with the advent of reverse wireless charging on smartphones, you can charge these smaller gadgets on the go which is really convenient. Also, brands like Realme have incorporated wireless charging into the Realme Buds Air which is probably one of the most affordable pairs of wireless earphones to come with support for wireless charging. It’s surely a step in the right direction.

Truly Wireless Future?

However, this brings us back to the initial question. Why hasn’t wireless charging made its way yet to more affordable smartphones? While features like a fingerprint scanner or fast charging were truly solving a problem and were essential breakthroughs, wireless charging, despite existing for so long has never been considered a must-have and is hence an easy feature for brands to skimp out on and save some money, and nobody is really complaining about it. With Apple rumored to be moving towards a completely port-less iPhone, the future is indeed completely wireless, but the tech to make it happen right now isn’t mature yet.